Hydraulic Terms P, Hydraulic phrases P, Hydraulic glossary P

Hydraulic Terms P speaks to hydraulic phrases P and hydraulic glossary P which are in common use in the hydraulic industry.

Pilot Operation Directional valve spools can be shifted with fluid pressure by either air or hydraulic. In these valves pilot pressure is applied to the two extreme spool lands if it is a 4 land spool or to separate pilot pistons if it is a 2 land spool.

Piping When you are connecting up a hydraulic system, use the tubing or pipe that is capable of handling heavy pressures and loads required by the hydraulic system. Pipes should have a minimum number of bends and fittings, should be securely fastened and clean. Iron pipes are not recommended because they have particles that will flake off and contaminate a system.

Piston A device used for converting hydraulic power to mechanical energy. In hydraulic pumps the piston is responsible for pushing down and pulling up the ram.

Hydraulic Terms P

Piston Motors A piston motor is a displacement motor which develops an output torque at its shaft by allowing hydraulic pressure to act on pistons. The rotating group of a piston motor basically consists of swahplate, cylinder barrel, pistons, shoeplate, shoeplate bias spring, port plate and shaft.

Piston Pump Piston pumps generate a pumping action by causing pistons to reciprocate within a piston bore. The pumping mechanism of a piston pump basically consists of a cylinder barrel, pistons with shoes, swashplate, shoeplate bias spring and port plate.

Piston Rod Speed The rod speed of a piston is determined by how quickly the volume behind the piston can be filled with liquid. The expression which describes piston rod speed (in/min) is gpm times 231 divided by piston area in square inches.

Plunger Pressure Gauge This is a gauge which consists of a plunger connected to system pressure, a bias spring, pointer and a calibrated scale calibrated in units of pressure.

PO Check Valve This is a pilot operated check valve.

Hydraulic Terms P

Port The internal or external terminus of a passage. The point where the fitting is attached.

Pour Point The pour point of a hydraulic fluid is the lowest temperature at which it will pour under an ASTM laboratory test and should be at least 20 F below the lowest expected operating temperature.

Power Work is done within a certain time. Power is the speed or rate at which work is done.

Power Unit A combination of pump, pump drive, reservoir, controls and conditioning components to supply hydraulic power to a system

Positive DisplacementPump A positive displacement pump will deliver a constant flow of liquid and will apply within limits the pressure required. This pump develops working energy which is kinetic energy, flow and pressure. This pump basically consists of a movable member inside a housing and has a plunger as the movable member. The shaft of the piston is connected to a prime mover (engine or electric motor) which is modified to produce a constant reciprocating motion of the plunger.

The inlet port is connected to a fluid reservoir. At inlet and outlet ports a ball allows liquid to flow only one way through the housing. After the housing is filled the plunger is pushed in. The ball at the inlet closes and the ball at the outlet port unseats. A decreasing volume is formed within the housing and the plunger applies the pressure necessary to move the liquid out into the system The constant cycling of the piston results in a pulsating rate of flow at whatever pressure is required.

Potential Energy Potential energy is that which is stored. It is waiting to be used, to change to a kinetic state when required. It has the ability to convert because of its physical makeup or position above a reference point.

Pressure The force per unit area, expressed in pounds per square inch (psi), bars, or atmospheres.

Pressure; Back The pressure encountered on the downstream or return side of a component.

Pressure Control Valve This valve has an internal moving part which is operated by pressure. When the pressure in a system reaches a certain level, the internal moving part connects or disconnects passages in a valve body allowing the liquid to follow another path.

Pressure; Cracking The pressure at which a pressure operated valve begins to pass fluid.

Pressure Filter A pressure filter is positioned in the circuit between the pump and a system component. The range of pressure line filters is from 40-30 micrometers.

Pressure Gauge It is a device which measures the intensity of a force applied to a liquid There are two types of pressure gauges used in hydraulic systems, Bourdon tube gauge and Plunger gauge.

Pressure; Maximum Rated The maximum pressure at which a component should be operated on a continuous basis, usually the relief valve setting at maximum flow rate.

Hydraulic Terms P

Pressure Reducing Valve A pressure reducing valve is usually a normally passing control valve. It operates by sensing fluid pressure after it has passed through the valve. As pressure downstream equals the setting of the valve, the spool is partially closed causing a restricted flow path. This restriction turns any excess pressure energy ahead of the valve into heat.

Pressure Relief Valves A pressure relief valve is a safety device and is required on all hydraulic systems. Once adjusted, the pressure relief valve opens whenever the pressure goes beyond the value set and allows oil to flow back to the reservoir.

Priority Flow Divider This is a bypass type pressure compensated flow control valve in which secondary flow is to an actuator instead of to tank.

Pumps The building block of any hydraulic system is the pump. The four most common designs are the vane, gear, gerotor and piston. All are well suited to common hydraulic uses with the piston design best suited for higher pressures. The variable displacement type is particularly well suited in circuits using hydraulic motors where variable speeds and the ability to reverse is needed.

Pump Unloading During idle time, when actuators are stalled, flow should not be dumped over a relief valve for more than a few seconds. Relief valves are designed to be used for short periods of time. If this is not done considerable heat will be added to the system.

Hydraulic Terms P



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